Laminated contact



Nov. 21 1939. I .1 i PAYETTE V 2,181-,083

LAMINATED CONTACT Filed Jan. 2, 1936 5 "Ra 2 l M W,

mema Nov. 21, 1939.

2,s,os3 V LAMNA'rEn CONTACT Joseph Arthur Payette, Attlebo'o, Mass., assignor, by mesne assignments, to Metals & Controls Corporation, Attleboro, Mass., a. corporation of Massaohusetts Application January 2, 1936, Serial No. 57,155' 2 Claims. (CI. zoo-166) This invention relates to' electrical contacts, and withregard to certain more specific features, to 'electrical contacts of laminated form.

This application is in part a continuatlon oi my application Serial No. 733,'719, filed July 5, 1934,

and entitled "Laminated contacts and the manufacture thereof."

Among the several objects of the invention may be noted the provision of-an electrlcalcontact' 10, which is made up in laminated form, the precious metal `content of the contact being thereby reduced, but without impairing the electrical efiiciency of the contact; a contact of the class described which has substantially as good heat dis- 15, sipation characteristics as contacts made of solid precious metal; a laminated contact of the class described which embodies a placement or distribution of the precious metal lar'ninae in such manner as to obtain a maximum wear-resistant life for the contact; and the provislon of an electrical contact which is particularly suitablefor attachment by spot or projection welding to its ultimate support. Other objects ,will be in part obvious and in part polnted out hereinafter. The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts, which will be exemplified in the structures hereinafter described, and the scope of the applicationoi 80 which will be indicated in the following 'claims.

In the accompanying drawing, in which is illustrated several' of various possible embodiments of the invention,

Fig. 1 is a trimetric view .of a laminated sheet stock for the manufacture of the contacts of the present invention;

Fig. 2 is a trimetric view of the sheet stock of Fig. 1 after it has been rolled to a suitable thickness; i Fig. 3 is a contact blank formed from the sheet stock ofFig. 2; I Fig. 4 is a vertical cross-sectional through the blank of Fig. 3; i Fig. 5 illustrates, in section, a stamping or coining operation on the blank of Fig. 4;

,Fig. 6 is a plan view of a finished contact made in accordance with the present invention; Fig. 7 is a vertical section taken substantially 5 along line 1-1 of Fig. 6;

tive shape to the blank of Fig. 3; i

Fig. 9 is a plan View of a contact made from the blank of Fig. .8;-

; 55 Fig. 10 is a viuv similar to Fig. 5, illustrating Fig. 8 is a trimetric view of a blank of alterna- 'an alternative manner of forming a contact button; i

- Fig. 11 is a vertical cross-section of the contact button made as in Fig. 10; and,

Fig. 12 is a trimetric View of a sheet stock usable alternatively with the sheet stock of Fig. 1. v similar reference characters indicate corresponding .parts throughout the several views of the drawing. v

Fine silver contacts are extensively used in o automatic and hand operated electric switches, having'been found particularly suitable for that purpose. These fine silver contacts are found in several forms, including rivets, or .buttons adapted for projection welding to their supports. w Upto the present time, the majority of such contacts have been made from solid fine' silver or other suitable metals. The present invention, in distinction, comprises forming the contact from laminated stock in such manner that the 20 silver 'protects the arcing surfaces and is economically disposed, being thickest at the position where contact is actually made, the remainder of the contact being formed of steel or other suitable ferrous base metal particularly chosen for ease in welding to the support member. It has been found that such a laminated contact is not only more economical to make, due to the saving of silver, but it also is a superior product in several respects.

` Fig. 1 of the drawing illustrates an assembly constituting the basic stock of the present invention, comprising' a' bar of silver l, a bar of base metal 2, which ispreferably a ferrous a-lloy, such as steel, and a thin sheet of metal 3, such as nickel, which prevents the silver I from diffusing into the steel 2, in accordance with the invention of Davignon Patent 1,571,541. These three layers are 'to be `joined to form the basis.

for the sheet stock from which the contacts of w the present invention are to be made. The surfaces of bars l, 2, and 3that are to be joined must be first machined so that they fit together i with a smooth, close fit, and then cleaned either mechanically or chemically or both, and then juxtaposed in the manner shown in Fig. 1.

It is preferable to directly weld the bars i,. i

2 and '3 without intermediate layers of solder.

but if solder is desired thin sheets of it are laid between the bars.

metal of the bars I and 3, as well as 2 and 3.'so

as to secure a good joint.`-'

In most cases it is-desirable to join the bars I, 2, and 3 in thicknesses considerably` in excess 5 of those ultimately desired, 'and then after joining to roll the blank to reduce its thickness. This facilitates the joining operations by reducing the area of the joint to be made. i

Fig. 2 represents the joihed bars of Fig. 1 after rolling out into a sheet of the desired thickness proportionate thicknesses of the bars I and 2 of for the contact blanks. The ratio of the thickness of the silver and the base metal in the sheet can be readily controlled to suit the needs of the particular case involved by regulating the the assembly of Fig. 1. By the time the rolling has taken place, the intermediate layer 3 is sopair of dies 5 and B' shown in Fig. 5. The bottom of the female die 5 is rounded; Thebottom of the male die 6 is likewise rounded, but at a some what greater radius of curvature, or it may be flat if desired. The male die 6 also includes a number (three, in the present instance) of holes or depressions As a result of the shape of the dies 5 and 6, the button 4 after having been stamped* therein, assumes the shape indicated in Figures 6 and 7. The silver layer l, it will be noted, has become thicker at the center and the edges have flowed to cover the entire sidesof the button, this taking place because the receptacle of thefemale die 5 is larger in diameter than the button blank and the silver is softer than the base metal layer. The base metal layer 2 has projections 8 extending from` the upper, concave surface thereof. The crowning 'action of the dies 5, and 8 provides most ofthe silver metal at the center, where it is subjected to th'e greatest use and wear, but a` portion is nevertheless positioned over the edges of the button. The projections 8 from the base metal layer 2, which may be varied in size, shape, and number, or in some cases entirely omitted, when provided are to facilitate the resistance welding operation by which the conflat r desired, V

to suit the needs'of the resistance welding oper-,

- tact is to be Secured to its support. The concavity of the back surface of the contact button is an optional feature providing a slight overhang which aids in protecting the support member from the a-c..` The back of the button jnay be either' with or without projections ation. a 4

The base metal layer 2 has been described as ferrous alloys or metals having a similarly high electrical resistance may-be used. It has been found that metals having a high electrical resistance weld much-more readily than those having a low resistance. It is believed that they engender the heat formation in a more localized manner in the region of the joint between the contact and its support, where it is needed, in resistance welding the contact to its support; The

0 contacts of the present invention are particularly designed for this purpose. Ingot ironihas a similar high electrical resistance, "at least, relatively higher than the silver contact racing.

Thus. by using arelatively high resistance fer-- -u rous metal as a hacking layer, contacts are' pro-.

a ferrous metal or alloy such as steel, but'other :2,-s,oss-

vided which are more suitable frwelding man' solid silver contacts, a more durable attachment of the contact,to its support is obtained, and diflicult'y with the contacts breaking loose under the pounding action of use is eliminated.

The laminated contact of the present invention is likewise superior to the prior solid silver button for the following additional reasons: The base metal of the laminated contact work-hardens to a much greater extent than the silver in gram. The cross grain is produced by' the stampins of the contact from rolled 'sheet stock. Prior all-silver contacts have usually been made by upsetting wire stock, which results in the presentation of an end grain at the contacting face.

Experiments have shown that the cross grain is much more wear-resisting than the end grain. Greater density of, the silver layer is also obtained by stamping the contact; the steel hacking providing a hard foundation.

The use of the base metal-layer does not de- `tract in' any way from the desirable properties' of a solid silver contact, since with the silver-base metal joint made in the manner described, .the flow of heat from the silver to the base metal at their interface is not impeded, and the conduc- 'tion of heat away from the contact surface is practically as good as 'that of a solid silver button. The electrical .'conductivity of the base metal layer is, by intention, not 'as good as' that of the silver layer, but as the body' of the contact is usually oversized from the conductivity standpoint, so asto provide mass for the absorption of heat caused by arcing as connection is broken, the reduction of electrical conductivity is of no great consequence. Further, the superiority of the weld of the button to its support, by reason of the greater suitability for welding of the hacking layer, so greatly increases the conductivity at this point that any decreased conductivity in the button itself is adequately compensated for.

' In stamping 'the circular blanks 4 of Flg.. 3

from the sheet stock oi' Fig. 2, a certain amount' of scrap will always result. This scrap may of course be saved and laterreflned to recover'the silver; as' an alternative the' blanks may be stampedinthe hexagonal form shown in Fle. 8, as such a form permitsmultiplication with less wastage. The hexagonal blanks 9 of Fig. 8 are then stamped as in Fig. 5, and the resulting contact buttons, shown in Figur-es 9 and 7 (the crosssection of the circular and hexagonal contacts are both the same. ,and illustrated by Fig. 7), may have substantially equal electrical capacity to the round contact buttons of Fig. 6 without ree quiring as much sheet stock, before blanking. per button.

The 'preferred form of the invention is that in which the silver. in the stamping operation, is forced to cover the edge of the button (as heretofore described). Howev'er, in some instances this is not necessary. Insuch event, the stamp-'- ing die 5 is provided with a recess ll (m. 10)' just large enough in 'diameter to 'receive the blank. By use of such a die, a button such as that shown lnFlg. 11, with no silver at the edge;

4 is obtained;

'While it is 'preferred to use a blllet or.blank &101.003

that all matter contained in the above descrlption or shown in the accompa'nying drawing shall u be interpretedas iliustrative and not in a limiting sense.

I claim: 7 l. An electrical contact button comprlsing a disc having a silver racing and a high electrlcal resistance ferrou metal hacking su'perflcialiy secured together, said bacldng having at least one projection extending therefrom adapted to facilitate weldlng said contact button to its support.

2. An electrical contact button comprleing a disc having a silver racing and a ten-qu: metal backing superlicially secured together. said terv rous metal hacking having at least one projection extending therefrom adapted to !acllitate welding said button to its support.

JO'SEPE .mram. ?nm 

